The invention relates to a method of operating an internal combustion engine having at least one mode of operation in which combustion substantially relies on autoignition of a compression ignitable homogeneous fuel/air mixture, more specifically of a gasoline/air mixture, the temperature in the combustion chamber being controlled by exhaust gas recirculation.
The major elements determining the combustion process in an internal combustion engine are the phase position of the combustion process, or rather of the start of combustion, the maximum rate of cylinder pressure rise and the peak pressure point.
In an internal combustion engine in which combustion substantially relies on autoignition of a compression ignitable homogeneous fuel/air mixture, these elements are determined by controlling the charge composition and the charge temperature history. These two values are in turn determined by a great number of influencing variables such as engine speed, fuel quantity, boost pressure, effective compression ratio, inert gas content of the cylinder charge and temperature of the component parts.
It has been found that the charge temperature plays a particularly important part in controlling the speed of the chemical processes taking place during the ignition delay period and during the very combustion. A very efficient means of increasing the charge temperature is to increase the residual gas content, meaning to increase the amount of not expelled, recirculated exhaust gases of the previous combustion cycle contained in the cylinder charge and intended to be used in the next cycle.